1. Field
Example embodiments relate to a thin film transistor (TFT), and more particularly to a junction field effect TFT.
2. Description of the Related Art
A thin film transistor (TFT) may be a switching device used, for example, in liquid crystal display devices, in organic electroluminescent (EL) display devices, or in memory devices, and may generally have a metal oxide semiconductor field effect transistor (MOSFET) structure as illustrated in FIG. 1.
Referring to FIG. 1, a conventional TFT may include a predetermined or given substrate 10, for example, silicon, on which a gate electrode 20 and a gate insulating layer 25 may be sequentially formed. A semiconductor layer 30 may be formed on the gate insulating layer 25 and on the substrate 10 as a channel layer, and a source electrode 40a and a drain electrode 40b may be formed on both sides of the upper surface of the semiconductor layer 30.
The gate insulating layer 25 may be formed of an oxide layer, usually through a heat process, and the semiconductor layer 30 may be formed of a metal oxide, for example, indium zinc oxide (IZO).
In the conventional TFT, a channel, that is, an electrical connection path of the source electrode 40a and the drain electrode 40b may be formed in the semiconductor layer 30 adjacent to the gate insulating layer 25 by applying a voltage greater than the threshold voltage Vt to the gate electrode 20. In other words, a voltage that may be applied to the gate electrode 20 determines whether the channel may be formed or not, and thereby switching may be determined by the channel.
However, when a portion of the semiconductor layer 30 that may be adjacent to the gate insulating layer 25 may be used as a channel in the conventional TFT, many defects may be present at an interface (portion A) of the gate insulating layer 25 and the semiconductor layer 30, which may result in a decrease in the mobility of carriers.
Thus, the conventional TFT having a portion of the semiconductor layer 30 adjacent to the gate insulating layer 25 as a channel, as illustrated in FIG. 1, may be limited in increasing operation speed and improving performance of the conventional TFT.
Also, in the conventional TFT, the gate insulating layer 25 may have to be charged to turn-on the TFT, thereby decreasing the operation speed and increasing power consumption. Moreover, in order to obtain a high quality gate insulating layer 25, a high temperature process may be required, which may deteriorate the properties of the conventional TFT, and may limit the available types of substrates that may be used. For example, a plastic substrate may not be used in a TFT manufacturing process that requires a high temperature process.